"So that could well be indicative that we are running into a fairly severe year with flu.

Dr Hampson says mortality rates could be higher this year than in previous seasons.

"It is just typically that when we get a major outbreak of H3N2 virus in the population, that we do see what we refer to as excess mortality," he said.

"Whether it just means we are having an early season or whether it is going to continue to rise, we can never be completely sure.

"But probably because we've got two different strains in the population compared with the last two or three years, it probably will continue to rise.

The World Health Organisation's Ian Barr says on average only one in five Australians receive a flu vaccination.

"Only 20 per cent of people get vaccinated in any one year," Mr Barr said.

"This year will be no different, so the majority of people are not vaccinated against influenza and they are relying on their previous exposures for their immunity, or they're just prepared to take that chance."

Director of Respiratory Medicine at the Royal Melbourne Hospital, Professor Lou Irving, says there are measures people can take to avoid contracting the flu.

"The warning is worth heeding in terms of precautionary measures such as making sure that the at risk people have been vaccinated and avoiding people who have got influenza," Professor Irving said.

"And if an individual develops influenza symptoms, they should see their doctor because there is an antiviral treatment that is safe and effective."

Doctors say it can take up to three days for the H3N2 vaccine to take effect and up to two weeks for it to adequately protect someone from the flu.